Live 3-D X-ray video of a fly’s muscles in mid-flight

Flies are incredibly agile on the wing, pulling off twists and turns that outstrip anything we’ve accomplished. Their flight is powered by two pairs of large muscles in their thorax which contract rhythmically to make their wings beat anywhere between 100 and 1000 times per second. Power is transferfed from these muscles to the wings by a hinge made of an intricate collection of steering muscles. Although the steering muscles make up less than 3% of the flight muscle mass, they very effectively direct the force produced by the larger muscles, thus guiding the fly’s aerial acrobatics. In a paper appearing in PLoS Biology, a team of scientists from the UK and Switzerland used a particle accelerator to record high-speed X-ray images of blowflies (Calliphora vicina) in flight, producing a 3-D video of the inside of the fly showing the muscles moving as it manuevered.

The detailed video enabled the team to follow the action of different muscles, giving them a more complete of how the hinge controls the power transfer to the wings. “The fly’s wing hinge is probably the most complex joint in nature, and is the product of more than 300 million years of evolutionary refinement,” said Dr Simon Walker of Oxford University, who was lead author of the study together with Daniel Schwyn. “The result is a mechanism that differs dramatically from conventional manmade designs; built to bend and flex rather than to run like clockwork.”

The flies were tied to a tether and spun in place while the team made the recordings. In response, the flies tried to turn in the opposite direction, giving the researchers a view of how the muscles cooperate to pull off a turn. “We found that blowflies have evolved a mechanism rather like the differential in a car,” explained Professor Graham Taylor. “Whilst the power delivered to the fly’s wings on each side remains the same, the fly effectively ‘brakes’ on one side by diverting excess power into a steering muscle specialized to absorb mechanical energy.” If you want a more thorough explanation of their findings, there’s an accompanying commentary in the same issue of PLoS Biology.

The team is hoping their findings will help improve the design of micro air vehicles and other micromechanical devices. The novel technique will also be useful in learning how flies manage some of their other manuevers, and perhaps even in studying some other impressive insect motions. Most of the time, I’m drawn to studies because of the implications of their data, but in this case, it’s the data itself — these amazing videos — which caught my attention and that I wanted to share with you.